1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image formed on an electrostatic latent image-supporting member.
2. Description of the Related Art
Conventionally, an image-forming method in which an electrostatic latent image formed on an electrostatic latent-image-supporting member such as a photosensitive member is developed by toner and the toner images are transferred onto a recording medium such as recording paper has been widely used in copying machines, printers, facsimiles, etc. This method has also been adopted in full-color image-forming apparatuses for reproducing a multi-color image by superposing plural color toners.
For such electrostatic latent image-developing toners used in various image-forming apparatuses, various characteristics are required so as to meet respective demands. For example, in an image-forming apparatus of the digital system, the area gradation system and the laser intensity modulation system have been adopted as a multi-gradation image-reproducing system. In both of the systems, toners having a high fluidity are required so as to reproduce images with superior gradation. In particular, in the laser intensity modulation system, a higher fluidity is required since reproduction with high gradation is carried out by changing the quantity of adhesion of toner in accordance with a difference in electric charges of latent images resulting from the modulation of the laser intensity.
However, there are various technical problems to be overcome in order to satisfy the above-mentioned characteristics. For example, in order to improve the fluidity, it is effective to externally add a fluidizing agent, such as silica fine particles and titanium oxide fine particles, to the toner, and to increase the amount of addition of the fluidizing agent. However, when the addition amount of the external addition agent increases, the amount of the external addition agent that passes through the cleaning blade, adheres to and is fixed to the surface of the photosensitive member also increases, resulting in such a serious problem that other toner components adhere to and are fixed to the photosensitive member with the external addition agent forming a core at the time of cleaning (which is referred to as BS (black spot) problem). In contrast, when the quantity of the external addition agent is reduced so as to prevent the occurrence of BS, the fluidity becomes insufficient, and toner aggregation occurs due to stress, etc. within the developing device during the repetition of printing processes, resulting in a problem of white voids in solid images.
A technique has been proposed in which, in order to prevent the occurrence of adhering and fixing (BS) to the photosensitive member, titanium oxide having a comparatively large particle size (grinding agent) (number average particle size: 1 to 3 .mu.m) are admixed with toner particles together with the above-mentioned fluidizing agent. With respect to the titanium oxide, it is general to use titanium dioxide particles produced by depositing titanium hydroxide in a titanium (IV) salt solution and calcing the deposited titanium hydroxide so as to obtain titanium oxide particles to be used. However, the toner obtained by the above-mentioned technique raises the problem of damaging the photosensitive member at the time of cleaningbytheuseof abladeduringrepeatedimage-formingprocesses, or at the time of transferring process by the pressed transferring drum in a full-color image-forming apparatus, etc. When the photosensitive member has been scratched, the blade cleaning process does not function properly, resulting in captured external addition agent and toner components and accumulation thereof. This tends to raise serious problems such as noise in the resulting images.